Braiding machines have long been used in industry, for example, to braid metallic wire into electrical or electronic cable as a protective armor or into hydraulic hose and cordage as a load bearing structure or into rope, either metal or non-metallic.
One of such braiding machines has been known as a may-pole type machine wherein shuttles carrying a bobbin are moved by horn gears or notched rotors on a deck with all of the shuttles following alternating semi-circular or arcuate paths around the braiding point. Half the shuttles travel in one direction around the braiding point following one alternating path while the other half of the shuttles travel in the opposite direction around the braiding point following another alternating path which crosses the first path at each alternating direction. As the two sets of shuttles travel in opposite directions around the braiding point each crossing the path of the other, strands leaving the bobbins are interwoven as they converge to the braiding point. With such maypole type braiders, the bobbins are normally rotatably mounted on an axis perpendicular to the path of movement of the shuttles and parallel to the axis of the workpiece. As such, during one half of the time, each bobbin is moving radially away from the workpiece and the other half of the time radially towards the workpiece at a rate sometimes faster than the strand is being taken up by the workpiece.
Associated with each bobbin is a strand carrying assembly. The strand carrying assembly is carried by the shuttle and includes both a tension controlling mechanism and a clutch mechanism. The tension controlling mechanism functions to maintain a constant tension on the strand as it leaves the bobbin and converges to the braiding point notwithstanding the movement of the bobbin toward and away from the workpiece. The clutch mechanism restrains the bobbin from rotating and dispensing a strand and periodically releases the bobbin when the tension controlling mechanism reaches the limit of its operation. Release of the bobbin permits additional strand to be unwound from the bobbin and withdrawn from the strand carrier through the tension controlling mechanism.
Heretofore, the bobbin, clutch and tension controlling mechanism have been cantilevered on the shuttle with the clutch and slack take-up mechanism positioned at one radial side of the bobbin, that is unsymmetrical relative to the bobbin axis. Because of this non-symmetry and the crowding of all the assemblies into a small space so as to make a compact braider, the entire assembly is fixedly mounted on the shuttle with the clutch and tension mechanism in a predetermined radial position so that the bobbins and associated mechanisms moving in opposite directions can readily pass in the limited space available without interferring one with the other. The diameter and capacity of the bobbin is limited by the space occupied on the shuttle by the clutch and tension controlling mechanisms. A limited bobbin capacity causes an inefficient frequency of interruptions to replenish strand supplies on the bobbins.
In these machines, the bobbin and associated mechanisms are subjected to two different types of forces as the shuttle moves from one semi-circular path to the other; namely, constantly reversing rotational forces about the bobbin axis and constantly reversing centrifugal forces on the cantilevered portion of the assembly. These constantly reversing forces create large stresses in the various parts of the braiding machine, which if too high will ultimately fatigue the materials resulting in cracks forming, and if the cracks are not discovered in time, will result in breakage and damage to the entire machine. These stresses are a square function of the speed of rotation of the shuttles around the workpiece. The maximum speed of braiding is severely limited by the need to limit this speed of rotation and thus the rate of braiding the workpiece.
Due to the high reversing rotational and centrifugal forces on the bobbin assemblies, failures occur if extremely strict maintenance procedures are not followed. In some cases failed parts between other moving parts cause an entire wipe-out of the braider. Such wipe-outs are extremely expensive not only in the repair of the parts, but in the down time required to repair the braider and its intended braiding operation.
A further problem with existing maypole type braiders has been the time required to replace a bobbin when its strand has been entirely dispensed. With existing machines it has been necessary to stop the machine, remove the bobbin, install a new bobbin, and then guide its strand through the tension controlling mechanism to the workpiece. Advancing th strand through the take-up mechanism while the carrying assembly is in the braider consumes a substantial amount of time, which in a 24 or 32 strand braider can add up to a substantial amount of down time.
Other disadvantages of existing strand carriers arise in the tension controlling mechanisms. In order to fit on a shuttle adjacent the bobbin and other components the tension controlling mechanism is a laterally compact, generally elongated structure fixed at one end to the shuttle. A strand roller is slidable in a guideway extending the length of the structure and is spring biased toward the shuttle end. The strand extends from the bobbin laterally across the shuttle to the sliding strand roller, which turns the strand to extend toward the other end where it exits the carrier. Tension in the strand extending around the sliding strand roller urges the roller against the spring biasing force. A generally constant rate of strand output from the carrier is maintained by sliding movement of the strand roller in the guideway as permitted by the spring biasing force in response to changes in external strand tension. Sliding strand rollers are known to comprise a pulley mounted on an axle extending laterally from a shoe carried in the guideway. This arrangement causes strand tension at the pulley to transmit a bending moment through the axle and into the shoe, which is then undesirably forced against the sides of the guideway instead of being forced only in the direction of movement along the guideway. An imbalance of forces at the sliding strand roller causes friction which not only decreases efficienty of operation, but also results in overheating of the machine despite efforts to lubricate the frictionally engaged moving parts. Furthermore, sliding strand rollers are known to hesitate or jam in the guide way and thus fail to maintain the desired tension in the strand, which if too high can break either the strand or the machine, and if too low causes slack to become entangled in other strands or moving parts.